364 FOOD AND DIGESTION 



juice and of the bile to the intestine is interfered with, the feces contain a 

 great excess of fat. 



Some recent experiments, however, tend to prove that the entire fat of the 

 food is changed in the intestine into fatty acids and glycerin; that the fatty 

 acids are entirely, or in part, changed to soaps ; and that these soaps, or mixture 

 of soaps and free fatty acids, are absorbed in solution. The chief facts favor- 

 ing this view are that: (i) The action of steapsin is sufficiently rapid to allow 

 the saponification of a full fatty meal within the ordinary period of digestion; 

 (2) histological examination has never shown that fat particles can pass into 

 a columnar cell, and none have ever been found in the broad striated border 

 of the cell; (3) the fat globules found in columnar cells after a fatty meal grow 

 steadily larger as the period of absorption progresses, indicating that they are 

 deposited from solution ; (4) the fatty acids are easily soluble in bile solutions, 

 and the solubility of the soaps is greatly increased by the presence of bile. 

 The fat constituents, according to this theory, are recombined in the columnar 

 cells to form neutral fats. 



Conditions which Influence the Action of the Pancreatic Enzymes. 



The various pancreatic enzymes are influenced by heat, by the presence of 

 an excess of digestion products, etc., in the same way as ptyalin and pepsin. 

 Pancreatic enzymes act in a neutral, but best in an alkaline solution. The 

 trypsin, strange to say, is quickly destroyed by the alkaline solution (Bayliss 

 and Starling). The pancreatic juice offers the special case of a secretion of 



FIG. 269. The Liver from Below and Behind. L. S., Spigelian lobe; L. C., caudate 

 lobe;L. Q., quadrate lobe; R.L., right lobe;L.L., left lobe; g. bl., gall-bladder; v.c.i., inferior 

 vena cava; ./., umbilical fissure; /. d. v., fissure of the ductus venosus; p, portal fissure with 

 portal vein, hepatic artery, and bile-duct. (Wesley, from a His model.) 



proenzyme which is stable in alkaline solution until acted on by enterokinase, 

 and the amount of kinase present will, therefore, markedly influence the 

 amount of digestion of protein per unit of time. 



The Secretions of the Liver. The liver, the largest gland in the body, 

 situated in the abdomen on the right side chiefly, is an extremely vascular 

 organ, and receives its supply of blood from two distant sources, viz., from 



